The present invention relates to a magnetoresistive head which is capable of coping with high density magnetic recording, and also to a magnetic storage apparatus.
In the conventional magnetic recording disk drive, a read/write separation type head is employed wherein the recording is performed using an inductive thin film head, while the read back is performed using a magnetoresistive head. This magnetoresistive head takes advantage of a magnetoresistive effect or a phenomenon that electric resistance varies depending on the external magnetic field, and is constructed, as shown in FIG. 2, comprising a substrate 21, on which a magnetoresistive element consisting of a magnetoresistive film 24, a domain control film 25 and electrodes 26; upper and lower shield films 22 and 28 for interrupting unnecessary magnetic field; and gap insulation films 23 and 27 for isolating the magnetoresistive element from the shield films 22 and 28 are mounted. As for the material for the gap insulation films 23 and 27, an Al2O3 film or an SiO2 film is predominantly employed. As for the material for the lower shield film 28 on the other hand, an NiFe-based alloy film such as Ni80Fe20 and Ni46Fe54; an FeAlSi-based alloy film; or Co-based amorphous film such as CoTaZr, CoNbZr and CoMoZr is conventionally employed (IEEE Transaction on Magnetics, Vol.32, No.1, January 1996, pp.149-155. HAMAKAWA et al., xe2x80x9cspin-valve heads utilizing antiferromagnetic NiO layerxe2x80x9d; or IEEE Transaction on Magnetics, Vol.35, No.2, March 1997, pp.149-155. HAMAKAWA et al., xe2x80x9cspin-valve heads using CrMnPt antiferromagnetic filmsxe2x80x9d).
Due to the recent trend to further enhance the density of magnetic recording, it is required to make narrower the interval between the lower shield film and the upper shield film for the purpose of enhancing the resolution of the magnetoresistive head. Therefore, it is required that the gap insulation film is formed thinner. In this case, there is a problem that if the dielectric strength of the gap insulation film is too low, short-circuit may be caused to occur between the magnetoresistive film or electrodes and the shield films. As mentioned above, although an Al2O3 film or an SiO2 film is mainly employed for the gap insulation film, if the film thickness thereof is made as thin as 50 nm or less, the properties of the film would be greatly influenced by the roughness of the film or the pin-hole that may be formed in the film, thereby sharply deteriorating the dielectric strength of the gap insulation film.
It has been made clear through the experiments conducted by the present inventors that, as far as the lower gap insulation film is concerned in particular, the magnitude of deterioration of this dielectric strength varies depending on the kinds of the lower shield film. Namely, where the lower shield film is entirely formed of a Co-based amorphous soft magnetic film, it is possible to ensure a sufficient dielectric strength of the lower gap insulation film even if the film thickness of the lower gap insulation film is fairly thinned as compared with the situation where the lower shield film is formed of a crystalline soft magnetic film such as an NiFe alloy film or an FeAlSi alloy film. However, there would be raised another problem when the lower shield film is formed of a Co-based amorphous soft magnetic film that due to the subsequent heat history of head processing, the soft magnetic characteristics of the lower shield film is caused to deteriorate by the changes in magnetic anisotropy of the lower shield film, thereby fluctuating the read output of the head.
The present invention has been made under the aforementioned problems in the prior art, and therefore, an object of the present invention is to provide a magnetoresistive head which is capable of suppressing the fluctuation of read output of the head while ensuring a sufficient dielectric strength of the shielding portions by making use of a Co-based material.
The present invention has been accomplished as a result of intensive studies on the relationship among the lower shield film, a material for the gap insulation film and dielectric strength.
Namely, the magnetoresistive head according to the present invention is featured in that it comprises a magnetoresistive film; a pair of electrodes connected to both sides of said magnetoresistive film; upper and lower gap insulation films sandwiching said magnetoresistive film therebetween; an upper shield film formed on said upper gap insulation film; and a lower shield film formed below said lower gap insulation film; and that it is characterized in that said lower shield film is formed of a 2-ply structure comprising an amorphous soft magnetic film which is disposed contacting with said lower gap insulation film and a crystalline soft magnetic film which is disposed away from said lower gap insulation film.
Since the lower shield film is formed of a composite film having a 2-ply structure comprising an amorphous soft magnetic film which is disposed to contact with the lower gap insulation film and a crystalline soft magnetic film which is disposed away from the lower gap insulation film as described above, it is possible, even if the film thickness of the lower gap insulation film is fairly thinned, to obtain a magnetoresistive head which is capable of ensuring a sufficient dielectric strength between the lower shield film and the magnetoresistive element, and at the same time, capable of suppressing the fluctuation of read output of the head.
As for the amorphous soft magnetic film for constituting part of the lower shield film, it would be preferable to employ an amorphous film containing Co as a main component, such as CoTaZr, CoNbZr, CoMoZr, CoTaHf, CoNbHf, CoMoHf, etc.
As for the crystalline soft magnetic film for constituting part of the lower shield film, it would be preferable to employ a crystalline film containing Ni and/or Fe as a main component, such as NiFe alloy film and FeAlSi alloy film.
The film thickness of the amorphous soft magnetic film should preferably be in the range of 3 nm to 500 nm.
As for the materials for the lower gap insulation film, either of Al2O3, SiO2 and a mixture of Al2O3 and SiO2 can be preferably employed. As for the film thickness of the lower gap insulation film, most prominent effects can be obtained when it is confined to not more than 30 nm.
A read/write separation type head exhibiting an excellent performance can be obtained by combining the aforementioned magnetoresistive head with an inductive thin film head.
The magnetic storage apparatus according to the present invention is featured in that it comprises a magnetic recording medium; a magnetic head for reading and writing data through said magnetic recording medium; a mechanism for positioning said magnetic head to a desired diametral portion over said magnetic recording medium while supporting said magnetic head; and a read/write signal processing system for processing read signals and write signals; and that it is characterized in that said magnetic head is constituted by a read/write separation type head comprising a combination of the aforementioned magnetoresistive head and an inductive thin film head.
According to the present invention, since a region of the lower shield film which is contacted with the lower gap insulation film is constituted by an amorphous soft magnetic film, while the opposite region of the lower shield film which is disposed away from the lower gap insulation film is constituted by a crystalline soft magnetic film, the initial growth of the lower gap insulation film is suppressed to thereby make it excellent in quality even if the film thickness thereof is fairly thin. As a result, the dielectric breakdown of the lower gap insulation film is deemed to be suppressed even if the film thickness thereof is fairly thin. As a matter of fact, even if the film thickness thereof is made as thin as 30 nm or less, a sharp decrease of the dielectric breakdown voltage cannot be recognized, thereby making it possible to provide the magnetic head giving high yield as compared with the case where the conventional single-layer crystalline soft magnetic film is employed. Additionally, when this read head is combined with a recording inductive magnetic head, it becomes possible to obtain a magnetic head or a magnetic storage apparatus, both being capable of coping with high density magnetic recording.